a. Field of the Invention
The present invention relates to a movie (video) on demand systems of the type wherein multiple clients are serviced by video streams delivered from a central video server.
b. Related Art
With the advent of digital video technology, it is feasible to provide video-on-demand services to a large number of clients over a geographically distributed network. The videos are stored on secondary storage devices (such as disks and tapes) on the server and delivered to the clients. Because of non-uniform demand for different movies, load imbalances amongst the secondary storage devices may occur. In such situations, the most heavily loaded secondary storage device can become a bottleneck.
One solution to the load balancing problem is to statically replicate popular movies on multiple secondary storage devices based on the expected load, such that the total demand for the movie can be spread among the devices having a copy of the movie. This is, however, expensive in terms of the storage space required. Additionally, it is difficult to determine exactly how much replication is required for any particular movie since, typically, the demand can not be exactly forecast. Static replication is also not well suited to dealing with the problem of time-varying load since the number of replicas needed may vary.
Dynamic replication is more effective on load surges that occur on a time scale comparable to the time to copy a video file or segment. In dynamic replication, movies or portions of movies are copied, as a function of present demand, from heavily loaded storage devices to more lightly loaded storage devices in order to reduce the load. The effectiveness of dynamic replication in dealing with sudden load surges is limited by the bandwidth of the secondary storage devices.